Many reptiles need sufficient lighting and some need a very specific type of UV light to thrive. These include all turtles and tortoises and the majority of lizards. Without exposure to UV light, these reptiles cannot produce Vitamin D3 effectively, leading to problems with calcium metabolism. By exposing the skin to natural sunlight or an artificial UV light source, the reptiles can produce the necessary Vitamin D3 within their bodies. Supplementation of Vitamin D3 via the diet is possible but not as effective. Since sunlight is a scarce resource in Britain and in any case, the crucial UVA And UVB rays are blocked by glass - most reptile keepers will need to invest in an artificial UV source.
Even if your reptile does not need UV light to maintain health – such as many snakes and nocturnal lizards - it is still important to provide a regular night-day cycle, similar to that in the wild, to prevent the animal experiencing stress.